1. Field of the Invention
The present invention relates to a display device using an organic light emitting element and a manufacturing method thereof, and more particularly to a display device using an organic light emitting element capable of keeping a stable light emitting property for a long period.
Note that the organic light emitting element in this specification indicates an element in which an organic compound layer is sandwiched between two electrodes to produce light emission. As the organic light emitting element, there is a light emitting element using an organic light emitting diode (OLED). The organic light emitting diode is a phosphor in which an organic compound layer is sandwiched between two electrodes, and a hole is injected from one electrode and an electron is injected from the other electrode so that the hole and the electron are combined in the organic compound layer to thereby produce light emission.
2. Description of the Related Art
Recently, a display device using an organic light emitting element is actively researched. In the case of the display device using the organic light emitting element, greater reduction in its weight and thickness is possible as compared with a conventional CRT and an application to various uses is being progressed. Since it is now possible to connect a mobile telephone, a personal digital assistant (PDA), or the like with the Internet, the amount of information to be displayed has dramatically increased, and the need for color display and high resolution of a display device is increased.
On the other hand, it is important for a display device incorporated in such a personal digital assistant to be reduced in its weight. For example, in the case of the mobile telephone, a product which weighs less than 70 g is currently on the market. For weight reduction, a review of most of parts to be used such as individual electronic parts, a case, and a battery is being conducted. However, in order to realize further weight reduction, it is also necessary to promote weight reduction of a display device.
A display device in which a pixel portion is composed of an organic light emitting element is of a self light emission type and does not require a light source such as a back light used in a liquid crystal display device. Thus, it is being greatly promised as means for realizing reduced weight and thickness.
With the organic light emitting element, blue color light emission is possible and a self light emission display device capable of full color display can be realized. However, in the organic light emitting element, various deterioration phenomena are recognized. which hinder the practical use. Thus, it is considered necessary to solve such a problem as soon as possible.
For example, a dark spot is a point defect of non-light emission, which is observed in a pixel portion, and is recognized as a problem for markedly degrading display quality. It is said that the dark spot is a progress type defect which increases even without operating the element, if moisture is present. It is considered that the dark spot is caused by an oxidation reaction of a cathode made of alkali metal.
Therefore, the display device using the organic light emitting element is constructed such that an element substrate on which a light emitting element is provided and a sealing substrate which is provided so as to oppose the element substrate are bonded together through a seal member having adhesion so that the light emitting element is not exposed to outside air including moisture. The sealing substrate is made of stainless steel or metal such as aluminum, which is easy to process. A dry agent is disposed in a concaved portion of the surface of the sealing substrate.
The seal member is mixed with a filler to control a gap between the element substrate and the sealing substrate. Thus, the seal member has both a function for bonding together the sealing substrate and the element substrate and a function for controlling the gap between the sealing substrate and the element substrate. Therefore. when the gap between the element substrate and the sealing substrate is set to be a general value of 10 xcexcm to 50 xcexcm, it is necessary to change the thickness of the seal member in accordance with the size of the gap.
Note that the shortest distance between the light emitting element and a surface of the sealing substrate opposing the light emitting element is called a gap between the sealing substrate and the element substrate, or simply a gap.
Now, the seal member for controlling the gap between the element substrate and the sealing substrate is made of an organic resin material and has higher moisture permeability than an inorganic material such as a glass material. For example, at a temperature of 60xc2x0 C. and a humidity of 90%, moisture permeability becomes 15 g/m2xc2x724 hr. to 30 g/m2xc2x724 hr. Even when the sealing substrate and the element substrate are sealed with the seal member, the organic light emitting element is deteriorated by a water vapor which is transmitted through the seal member and penetrated in a sealed region. The amount of water vapor to be transmitted through the seal member is determined by the product of an area of the seal member to be exposed to outside air and moisture permeability. Thus, it is desirable that the area of the seal member to be exposed to outside air is small. That is, it is desirable that the thickness of the seal member is minimized.
As the thickness of the seal member is increased, the amount of moisture to be transmitted through the seal member is increased. Even if the dry agent is provided, the light emitting element is deteriorated by the moisture which is not absorbed by the dry agent. That is, an object of the present invention is to reduce the amount of moisture to be transmitted through the seal member.
Also, a method of thinning a glass substrate may be conceived to achieve weight reduction of the personal digital assistant. However, the glass substrate is more likely to break as it becomes thinner and its shock resistance is reduced. In particular, when the sealing substrate made of metal and the element substrate made of glass are bonded together, because of a difference in thermal expansion coefficient, a distortion is caused due to a sudden change in a temperature and a crack is caused in the substrate made of glass. However, this becomes a critical defect in the case where such a substrate is used for the personal digital assistant.
Therefore, an object of the present invention, is to prevent the breaking of the substrate to improve the durability thereof in the case of a construction in which the glass substrate is reduced in thickness to realize a thin display device.
Thus, although the display device composed of the organic light emitting element is very effective for weight reduction of a display device, there remain problems to be solved in order to ensure the reliability of the organic light emitting element.
The present invention relates to a technique for solving such problems and an object of the present invention is to provide a display device using an organic light emitting element having high reliability and a manufacturing method thereof.
As the substrate made of glass has become thinner, when the element substrate made of glass and the sealing substrate made of metal are bonded together, because of a difference in a thermal expansion coefficient, the possibility that the element substrate made of glass is broken due to a sudden change in a temperature becomes high. In order to prevent this, according to the present invention, a substrate made of glass is used for the element substrate and the sealing substrate to obtain an identical thermal expansion coefficient. Thus, resistance thereof against a sudden change in a temperature is increased, and thus the object of the present invention is attained.
Further, according to the present invention, the surface of the sealing substrate made of glass is processed to have a concaved portion and a dry agent is disposed in the concave portion. Thus, as a conventional case, the dray agent can be provided in a sealed space surrounded by the element substrate, the sealing substrate, and the seal member to capture moisture which is transmitted through an adhesion member and penetrated in the sealed space. Calcium oxide, barium oxide, or the like can be suitably used for the dry agent. The dry agent may be provided on, for example, a driver circuit. Then, since the dry agent is present close to the light emitting element in a sealed region between the element substrate and the sealing substrate, penetration of moisture to the light emitting element can be reduced. Thus, stability of the light emitting element can be improved. For example, a dark spot caused by oxidation of a cathode can be reduced.
Also, according to the present invention, the sealing substrate made of glass is processed so that an outer edge portion of the sealing substrate protrudes in a convex shape. The gap between the element substrate and the sealing substrate is controlled by the convex portion. Then, since a layer having adhesion which is provided between the element substrate and the sealing substrate is required to have only a function for bonding the element substrate and the sealing substrate together, a function for controlling the gap becomes unnecessary. Thus, the thickness of the layer having adhesion can be made as small as possible as its material permits. Therefore, the amount of moisture which is transmitted through the layer having adhesion and penetrated in the sealed region can be reduced, whereby an object of the present invention, that is, reduction of the amount of moisture transmitted through the layer having adhesion, is attained. It is desirable that the thickness of the layer having adhesion (adhesion member) is 10 xcexcm or less, preferably, 1 xcexcm or less.
An abrasive machining method (sandblast method) can be used as a method of processing the surface of the sealing substrate. The abrasive machining method is a technique of blasting sands, fine steel billets and the like with compressed air to process the surface of a substrate made of glass.
One example of the construction of the present invention will be described using FIGS. 8A to 8C. FIGS. 8A to 8C are cross sectional views of a display device using an organic light emitting device of the present invention.
FIG. 8A shows an example where, in a display device constructed by bonding together an element substrate and a sealing substrate through a layer having adhesion, the surface of the sealing substrate is processed and a dry agent and a permeable film are provided in a sealed region. A first substrate 101 and a second substrate 102 are made from a translucent substrate, for example, a glass substrate. The first substrate is the element substrate on which an organic light emitting element is provided in a display region 129. The second substrate is the sealing substrate, and the surface thereof is recessed by processing. A dry agent 107 and a permeable film are disposed thereon. Note that, when light emitted from the organic light emitting element is picked up from the sealing substrate side, it is desirable the dry agent and the permeable film be provided outside the display region.
Note that, in the present invention, a region of the second substrate located on the same plane as a portion in which a layer 106 having adhesion is bonded to the second substrate is a first region 103 of the second substrate. Also, a region which is concaved relative to the first region is a second region 104. Further, a region which is concaved relative to the second region is a third region 105. In other wards, when a surface of the second substrate opposing the organic light emitting element is taken as the front surface and it is viewed from the rear surface of the second substrate, the first region is protruded in a convex shape relative to the second region and the third region.
The dry agent 107 is provided in the third region 105. A granular material or a flat sheet material can be also used for the day agent. For filling the dry agent, it is preferable that the third region is recessed by 50 xcexcm to 150 xcexcm relative to the second region.
The permeable film having high moisture permeability and having water vapor permeability is composed of an adhesive layer 125, a porous layer 126, and a base member 127. In order to contain the dry agent in the third region, the permeable film is attached with the adhesive layer 125 contacting with a part of the second region. The permeable film composed of the adhesive layer, the porous layer, and the base member, has a thickness of 150 xcexcm to 300 xcexcm. Also, it is desirable that the first substrate is located at a distance 10 xcexcm to 50 xcexcm or more apart from the surface of the base member constituting the permeable film so that the permeable film is not in contact with the first substrate. Thus, it is desirable that the second region is recessed by 160 xcexcm to 350 xcexcm relative to the first region.
Both an ultraviolet light curable resin and a heat curable resin can be used as the layer 106 having adhesion for bonding the element substrate and the sealing substrate together. The amount of moisture entering into the sealed region is determined by the product of an area of the layer having adhesion which is exposed to outside air and moisture permeability. Thus, it is desirable that the thickness of the layer having adhesion is minimized to reduce the area exposed to outside air.
According to the present invention, since the outer edge portion (first region) of the second substrate is protruded in a convex shape, the gap between the first substrate and the second substrate can be determined by the height of the convex portion of the outer edge portion of the second substrate. The layer having adhesion is not required to have a function for controlling the gap and thus may be used only to facilitate bonding of the first substrate and the second substrate. Thus, the layer having adhesion can be made as thin as possible insofar as its material permits.
Next, another example of the present invention is indicated. The present invention described below adopts a construction which takes into consideration not only the reduction of moisture which is transmitted and enters through the layer having adhesion but also the reduction of the amount of moisture left in a dry gas in the sealed region.
FIG. 8B is a cross sectional view of an organic light emitting element. When compared with FIG. 8A, a difference from FIG. 8 is that the gap between the first substrate and the second substrate is made smaller at 10 xcexcm to 50 xcexcm in the display region 129. The permeable film has a thickness of 150 xcexcm to 300 xcexcm and the gap having such a large thickness is unnecessary in the display region in which the permeable film is not provided. When the gap in the display region which takes up a predominantly large area of a display device is reduced to 3% to 50% as compared with that in FIG. 8A, a volume of a sealed space, that is, a volume of the dry gas is reduced, and the total amount of moisture left in the gas is reduced as a result.
FIG. 8C shows an example in which a flat sheet dry agent 107 is disposed in the third region 105 of the second substrate 102. Calcium oxide or the like is preferably used for the flat sheet dry agent.
In order to prevent mixing of fine powder into the display region which occurs when the dry agent is partially peeled off or otherwise damaged due to a shock applied thereon, adhesives 109 are provided in several locations on the surface of the dry agent and a porous film 108 having a thickness of 10 xcexcm to 30 xcexcm is attached to the dry agent through the adhesives 109. Thus, when the dry agent is covered with the porous film, fine powder produced due to a mechanical shock can be contained inside the porous film. It is preferable that the porous film are hollowed in a circular shape in two or more locations to expose the dry agent, an adhesive 110 is applied to the thus exposed portions. whereby the dry agent and the second substrate are bonded to each other. The thickness of the adhesive can be set to be 1 xcexcm to 5 xcexcm by controlling the amount of the adhesive to be applied onto the surface of the dry agent. In the case of FIG. 8C, it is desirable that a thickness of the porous film, a thickness of the dry agent and a thickness of the adhesive are adjusted so that the dry agent and the porous film can be received in the third region recessed by 50 xcexcm to 150 xcexcm relative to the second region.
In the cases of FIGS. 8A and 8B, in order not to crush the permeable film due to weight of the dry agent, it is required that the base member 127 having a thickness of 100 xcexcm to 150 xcexcm is provided in contact with the porous film 126 having a thickness of about 10 xcexcm to 70 xcexcm. Thus, the thickness of the base member and the thickness of the porous film needs to be increased to improve a mechanical strength of the permeable film. Further, since the adhesive layer 125 having a thickness of 40 xcexcm to 80 xcexcm is required for adhering the film to the substrate, the overall thickness of the permeable film becomes as large as 150 xcexcm to 300 xcexcm. Thus, the amount of moisture left in the gas in the sealed space is increased in correspondence with a volume occupied by the permeable film.
However, in the case of FIG. 8C, the film is only required to cover the dry agent and needs not to have high mechanical strength. Thus, even when a thin porous film having a thickness of 10 xcexcm to 30 xcexcm is used, there is no problem for practical use. Also, a volume of the sealed space can be reduced due to the reduced thickness of the film. To cover the dry agent, the porous films are provided on an upper surface (surface opposing the second substrate) of the dry agent and on a lower surface (surface opposing the first substrate) thereof. Thus, when the porous film having a thickness of 10 xcexcm to 30 xcexcm is used, the thickness of the porous film within the gap becomes twice as large, that is, 20 xcexcm to 60 xcexcm. Even so, the thickness of the porous film within the gap is made smaller than the thickness of permeable film. If the amount of dry agent is the same, a volume of the sealed region can be reduced with the construction shown in FIG. 8C, and thus the amount of moisture left in the gas becomes small. This leads to the suppression of oxidation reaction of the cathode due to moisture and the useful life of the display device can be increased.
Note that, in the case of FIG. 8C, it is preferable that the second region 104 is recessed by 10 xcexcm to 50 xcexcm relative to the first region so that the gap between the first substrate and the second substrate in the display region is set to be 10 xcexcm to 50 xcexcm.
Also, in the present invention, since the sealing substrate and the element substrate are translucent, light emitted from the organic light emitting element provided on the element substrate may be emitted toward either the sealing substrate side or the element substrate side. This can be freely designed in consideration of a size of the light emission area of the organic light emitting element and the like.
The present invention based on the above descriptions is as follows.
According to a first aspect of the present invention described in this specification, there is provided a display device comprising a first substrate on which an organic light emitting element is provided and a second substrate which is translucent, the first substrate and the second substrate being bonded together through a layer having adhesion, characterized in that a surface of the second substrate opposing the first substrate includes a first region and a second region, the first region is adhered with the layer having adhesion, and the second region is located inside the first region and is concaved relative to the first region.
In the first aspect of the present invention described in this specification, a portion of the sealing substrate to which the layer having adhesion is provided is made convex to the element substrate. Thus, a gap between the first substrate and the second substrate can be determined by a convex portion of the second substrate and the layer having adhesion can be used only for the purpose of bonding the first substrate and the second substrate together.
According to a second aspect of the present invention described in this specification, there is provided a display device comprising a first substrate on which an organic tight emitting element is provided and a second substrate which is translucent, the first substrate and the second substrate being bonded together through a layer having adhesion, characterized in that: a surface of the second substrate opposing the first substrate includes a first region, a second region, and a third region; the first region is adhered with the layer having adhesion; the second region is located inside the first region and concaved relative to the first region; the third region is located inside the second region and concaved relative to the second region; and a dry agent is provided in the third region.
In the second aspect of the present invention described in this specification, since a portion of the second substrate to which the layer having adhesion is adhered is convex, the sealing substrate has a function for controlling the gap, as in the first aspect of the present invention described in this specification. Further, the dry agent is provided in a concaved portion of the surface of the second substrate to capture moisture penetrated in the sealed region. Thus, the stability of the organic light emitting element is ensured for driving over a long period of time.
According to a third aspect of the present invention described in this specification, there is provided a display device characterized in that, in the second aspect of the present invention described in this specification, a permeable film is adhered to a part of the second region so that the dry agent is contained in the third region.
As in the case of the third aspect of the present invention described in this specification, a permeable film may be used as means for providing the dry agent in the third region.
According to a fourth aspect of the present invention described in this specification, there is provided a display device comprising a first substrate on which an organic light emitting element is provided, a layer having adhesion for enclosing with a gap an area surrounding a region in which the organic light emitting element is provided on the first substrate, and a second substrate which is translucent, the first substrate and the second substrate being bonded together through the layer having adhesion, characterized in that: a surface of the second substrate opposing the first substrate includes a first region, a second region, and a third region; the first region is adhered with the layer having adhesion; the second region is surrounded by the first region and concaved relative to the first region; the third region is located between the layer having adhesion and an upper portion of the region in which the organic light emitting element is provided and is concaved relative to the second region; and a dry agent is located in the third region.
In the fourth aspect of the present invention, a difference from the second aspect of the present invention described in this specification is that the dry agent is provided only in a region outside the display region.
According to a fifth aspect of the present invention described in this specification, there is provided a display device characterized in that, in the fourth aspect of the present invention described in this specification, a permeable film is provided between the layer having adhesion and the upper portion of the region in which the organic light emitting element is provided, and the permeable film is adhered to a part of the second region to thereby contain the dry agent in the third region.
As in the case of the fifth aspect of the present invention described in this specification, a permeable film may be used as means for providing the dry agent in the third region. The permeable film is preferably disposed outside the display region.
According to a sixth aspect of the present invention described in this specification, there is provided a display device characterized in that, in the third or the fifth aspect, the permeable film adhered to the second region is fit between a plane which is contact with the first region and a surface on which the permeable film is adhered to the second region. In other words, it is required that the permeable film is at least not in contact with the first substrate.
According to a seven aspect of the present invention described in this specification, there is provided a display device characterized in that, in the second aspect of the present invention described in this specification or in the fourth aspect of the present invention described in this specification, a difference in height between a bottom portion of the second region which is concaved relative to the first region and the first region is 10 xcexcm to 50 xcexcm. One example of the seven aspect of the present invention described in this specification has been described already using FIG. 8C.
According to an eighth aspect of the present invention described in this specification, there is provided a display device characterized in that, in the third aspect of the present invention described in this specification or in the fifth aspect of the present invention described in this specification, a difference in height between a bottom portion of the second region which is concaved relative to the first region and the first region is 160 xcexcm to 350 xcexcm. One example of the eight aspect of the present invention has been described already using FIGS. 8A and 8B.
According to a ninth aspect of the present invention described in this specification. there is provided a display device characterized in that, in any one of the first through eighth aspects of the present invention described in this specification, a difference in height between a bottom portion of the third region which is concaved relative to the second region and the second region is 50 xcexcm to 150 xcexcm. One example of the ninth aspect of the present invention described in this specification has been described already using FIGS. 8A to 8C.
According to a tenth aspect of the present invention described in this specification, there is provided a display device characterized in that, in any one of the first through ninth aspects of the present invention described in this specification, the first substrate is a glass substrate.
According to an eleventh aspect of the present invention described in this specification, there is provided a display device characterized in that, in any one of the first through ninth aspects of the present invention described in this specification, each of the first substrate and the second substrate is a glass substrate.
The shock resistance of the substrate decreases as it becomes thinner. Thus, when substrates are made from different materials, a crack is caused in a substrate made of glass due to a sudden change in a temperature. This is a phenomenon resulting from a difference in thermal expansion coefficient. However, when the first substrate and the second substrate are made of the same material as in the case of the eighth aspect, occurrence of a crack due to a thermal shock can be prevented.
According to a twelfth aspect of the present invention described in this specification, there is provided a display device characterized in that, in any one of the first through eleventh aspects of the present invention described in this specification, a thickness of the layer having adhesion is 10 xcexcm or less.
According to the present invention, since it is unnecessary to keep the gap by the layer having adhesion, the thickness of the layer having adhesion can be minimized. It is particularly desirable that the thickness of the layer having adhesion be set to 10 xcexcm or less in order to suppress the penetration of moisture in the sealed region.
According to a thirteenth aspect of the present invention described in this specification, there is provided a method of manufacturing a display device in which a first substrate and a second substrate which are translucent are bonded together through a layer having adhesion and an organic light emitting element is provided in the first substrate, characterized by comprising: a first step of setting a region of the second substrate to which the layer having adhesion is adhered as a first region and providing a first mask in at least the first region; a second step of digging the second substrate by an abrasive machining method to form a second region which is concaved relative to the first region; a third step of removing the first mask; a fourth step of providing a second mask in a region of the second substrate in which al least the first mask was provided and a region located above a region in which the organic light emitting element is provided and digging the second substrate by an abrasive machining method to thereby form a third region which is concaved relative to the second region; and a fifth step of providing a dry agent in the third region.
According to a fourteenth aspect of the present invention described in this specification, there is provided a method of manufacturing a display device characterized by further including, in the thirteenth aspect of the present invention described in this specification, a sixth step of providing a permeable film in the second region after the fifth step.
As a method of providing the dry agent in the third region, there are a method of adhering the dry agent to the second substrate and a method of adhering an adhesive layer of the permeable film to the second region to thereby contain the dry agent in the third region. The fourteenth aspect of the present invention described in this specification is a method used for the latter method.
According to a fifteenth aspect of the present invention described in this specification, there is provided a method of manufacturing a display device characterized in that, in the fourteenth aspect of the present invention described in this specification, a digging depth of the second substrate in the second step is larger than a thickness of the permeable film.
According to a sixteenth aspect of the present invention described in this specification, there is provided a method of manufacturing a display device characterized in that, in the thirteenth aspect of the present invention described in this specification, the digging depth in the second step is 10 xcexcm to 50 xcexcm. According to the sixteenth aspect of the present invention described in this specification, by processing the surface of the second substrate in the structure shown in FIG. 8C, for example, the second region can be recessed by 10 xcexcm to 50 xcexcm relative to the first region.
According to a seventeenth aspect of the present invention described in this specification, there is provided a method of manufacturing a display device characterized in that, in the fourteenth or the fifteenth aspect of the present invention described in this specification, the digging depth in the second step is 160 xcexcm to 350 xcexcm. According to the seventeenth aspect of the present invention described in this specification, in the structure shown in FIG. 8A or 8B, the second region 104 can be recessed by 160 xcexcm to 350 xcexcm relative to the first region 103.
According to an eighteenth aspect of the present invention described in this specification, there is provided a method of manufacturing a display device characterized in that, in any one of the thirteenth through seventeenth aspects of the present invention described in this specification, the digging depth in the third step is 50 xcexcm to 150 xcexcm. According to the eighteenth aspect of the present invention described in this specification, as shown in FIGS. 8A to 8C, the third region 105 in which the dry agent is provided can be recessed by 50 xcexcm to 150 xcexcm relative to the first region 104.
According to a nineteenth aspect of the present invention described in this specification, there is provided a method of manufacturing a display device characterized by further including, after the fifth step in the thirteenth through sixteenth aspect of the present invention described in this specification, a sixth step of bonding the first substrate and the second substrate together through the layer having adhesion and a seventh step of cutting the first substrate and the second substrate by a gas laser.
According to a twentieth aspect of the present invention described in this specification, there is provided a method of manufacturing a display device characterized by further including, after the sixth step in any one of the fourteenth through sixteenth aspects of the present invention described in this specification, a seventh step of bonding the first substrate and the second substrate together through the layer having adhesion and an eighth step of cutting the first substrate and the second substrate by a gas laser.
According to a twenty-first aspect of the present invention described in this specification, there is provided a method of manufacturing a display device characterized in that, in the nineteenth or twentieth aspect of the present invention described in this specification, the gas laser is a CO2 laser.
In accordance with another aspect of the present invention, a light emitting device of the present invention includes a first substrate and a second substrate opposed to each other and at least a light emitting layer interposed therebetween where the light is emitted out from the light emitting device through the second substrate and an inner surface of the second substrate is provided with minute unevennesses in order that outside light is prevented from reflecting at the interface between the second substrate and a sealed space and in an interface between the second substrate and air. Further, the heights of the minute unevennesses are set to be 0.1 xcexcm to 3 xcexcm, preferably, 0.1 xcexcm to 0.5 xcexcm. In order to prevent diffraction, it is preferable that the unevennesses having different curvatures are provided to improve scattering property. Taking the spacing (pitch) between the convex portions as X, it is preferable to set X=0.05 to 1 xcexcm (more preferably between 0.3 and 0.8 xcexcm). In other words, by setting the pitch of the convex portions to be nearly equal to the wavelength of visible light, diffuse reflection (irregular reflection) of the reflected light can be made to occur effectively.